Bypass dart and assembly

ABSTRACT

A plunger assembly for down-hole use in a well. In one embodiment, the plunger assembly comprises a plunger having a first and second end, a cage attached to the second end of the plunger, and a dart disposed within the cage having a body with at least two surfaces, where one surface is a raised surface relative to the other, lower surface.

BACKGROUND

1. Technical Field

Embodiments of the subject matter disclosed herein relate to an improved bypass dart and assembly, and methods of operating and using the same.

2. Discussion of the Background

It is well known that production from oil and gas wells can suffer due to the build-up of fluids at the bottom of the well. See e.g., U.S. Pat. No. 6,148,923, which is incorporated herein by reference. Various methods and devices have been developed to remove those fluids so as to improve the well's productivity.

One such device is known as a plunger, of which there are many variants known to those skilled in the art. For example, an auto-cycling plunger operates as follows: (1) it is dropped into the well (at the well's surface), (2) it free-falls down the well until it stops upon impact with the bottom of the well, and (3) it thereafter is caused (by pressure in the well) to travel back toward the surface of the well, pushing a “load” of liquid above it for removal at the well's surface. The plunger then is allowed to repeat that cycle, thereby ultimately removing enough fluid from the well to improve its production.

A number of problems have arisen from the use of prior art plungers. For example, due to the typically great distance between the surface and bottom of a well, the plunger travels at a great rate of speed when—due to its free-fall—it reaches and strikes the bottom of the well. Impacts between the plunger and the bottom of the well can be violent; they often are so violent that damage occurs (either immediately or over time due to repeated use) to either the plunger and/or whatever it strikes at the bottom of the well. As another example, the repeated cycling of the plunger causes at least certain of its parts eventually to wear out.

Damage to plungers due to impact and/or wear are prevalent in prior art “dart” bypass plungers. A “dart” bypass plunger is a well-known plunger that operates by free-falling down a well when its dart is in its open position, i.e., the dart is not seated so as to plug the otherwise hollow central passage of the plunger. This allows for the plunger to fall at a faster rate, and can eliminate the need to stop the flow of the well during the decent. When the plunger strikes the bottom of the well, the dart is forced upward into a seated position in the bottom portion of the plunger, so that the top of the dart plugs or otherwise blocks gas or fluids from passing up through the hollow center of the plunger. This blocking action performed by the dart causes pressure to build up below the plunger, eventually lifting the plunger and an amount of liquid above it to the surface of the well, where the liquid is removed and the dart is forced out of its sealed position in the plunger (usually by a metal rod in the well's lubricator), thereby causing the plunger to free-fall back down the well to start another cycle.

While the operation of dart bypass plungers is well know to those skilled in the art, it is similarly well-recognized that the dart employed by such plungers cannot be allowed to freely move between its open and closed position in the plunger since if that were the case the dart would: (1) prematurely move to its closed position as the plunger free-falls down the well, or first strikes enough liquid or upwardly flowing gas to cause it to close; or (2) prematurely move to its open position (due to gravity or the force applied by liquid above it) as the plunger rises in the well. Either instance will cause the plunger to malfunction or at least operate less efficiently. Accordingly, several prior art techniques have been used to restrict the otherwise free movement of the dart between its open and closed position in the plunger.

One technique for restricting movement of the dart between its open and closed position is placing two or more metal plates around the outside of the dart, where friction between the metal plates and the dart is applied by wrapping one or more flexible o-rings around the metal plates (see e.g., U.S. Pat. No. 7,438,125). The flexibility in the o-rings is designed to impart enough friction between the metal plates and the outside surface of the dart that the dart is held in its desired open or closed position until the plunger reaches the top of the well (where the lubricator forces the dart from its closed to its open position) or reaches the bottom of the well (where the impact between the dart and the bottom of the well forces the dart from its open to its closed position). This technique has proven unsatisfactory to the inventors of the present invention at least because the metal plates wear, creating a larger inside diameter, so that the same o-ring compression applies less resistance on the dart, and thereby creating insufficient force to keep the dart in position.

Another technique for restricting movement of the dart between its open and closed position is by employing a clutch (around the dart) comprised of one or more c-clips disposed in the body of the plunger's cage housing the dart, so that the clutch engages the outside surface of the dart. While the c-clips apply friction to the dart that restricts its movement similar to the metal plates described above, this technique has proven unsatisfactory to the inventors of the present invention at least because the constant force applied by the dart to the c-clips causes the c-clips to were out too rapidly. Further, because the c-clips typically cannot be replaced without damaging the plunger, the useful life of the plunger itself can be limited by the life of the c-clips.

As indicated above, still other defects (or limitations) in prior art dart bypass plungers relates to damage imparted to them by their repeated collisions with the top and the bottom of the well. These collisions typically first cause failures at the weakest part(s) of the plunger and often at locations on the plunger closest to such collisions. For example, as is well known by those skilled in the art, prior art dart bypass plungers often have a cage at the bottom of the plunger for housing the dart. Such cages typically are attached to the plunger by a threaded connection. The cage also typically has a threaded cap at its end opposite the threaded connection to the plunger. When the plunger strikes the bottom of the well, these threaded connections—and especially the threaded connection at the cap, which is closest to the plunger's point of impact with the bottom of the well—typically are the first to fail as a result of the repeated impacts and, thereby, prematurely end the useful life of the plunger.

Finally, different working environments impart still other limitations on prior art dart bypass plungers. For example, environments that are sandy or otherwise corrosive can cause premature failure of the plunger by clogging the passageways between the dart and its cage so much so that (1) the abrasiveness imparted by sand particles can cause premature wear of the clutch disk mechanism and/or the cage's o-ring (i.e., the mechanism that keeps the dart in its open or closed position) and/or (2) by clogging the passageways so much that the dart no longer appropriately slides between its open and closed position.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate one or more exemplary embodiments of the present invention. In the drawings:

FIG. 1 is an assembly diagram of one embodiment of a dart bypass plunger;

FIG. 2 is a cross-sectional diagram of one embodiment of a dart bypass plunger;

FIG. 3 is an assembly diagram of one embodiment of a dart for a dart bypass plunger;

FIG. 4 is an assembly diagram of another embodiment of a dart for a dart bypass plunger;

FIG. 5 is a cross-sectional diagram of one embodiment of a dart for a dart bypass plunger;

FIG. 6 is a cross-sectional diagram of one embodiment of a dart bypass plunger;

FIG. 7 is a cross-sectional diagram of one embodiment of the cage and dart portion of a dart bypass plunger;

FIG. 8 is a cross-sectional diagram of one embodiment of a dart bypass plunger;

FIG. 9 is a cross-sectional diagram of one embodiment of the cage and dart portion of a dart bypass plunger

DETAILED DESCRIPTION

The following description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.

Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” (or variants thereof) in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiment. The invention, however, is not limited to any one embodiment.

FIG. 1 illustrates an exemplary embodiment of the present invention. FIG. 1 shows dart bypass plunger 100, consisting generally of plunger body 110 and cage 120. FIG. 2 depicts a cross-section of dart bypass plunger 100.

As best shown by FIG. 2, the plunger has a generally hollow interior 200 so that liquid and/or gas can flow there-through when the plunger is deployed in a well. FIG. 2 also shows cage 210 (in threaded engagement with the plunger body near the bottom portion thereof) housing dart 220. In this embodiment, cage 210 is unitary in nature in that, while it is attached to the plunger body using threads, it has no other separate piece or component attached thereto using threads.

As shown, dart 220 is slidably mounted in cage 210 so that it can be positioned in at least an open or closed position relative to the bottom opening of the plunger. For example, the dart's open position exists when dart 220 is positioned so as to allow gas or liquid to flow substantially freely through the generally hollow interior 200 of the plunger when the device is deployed in a well. The dart's closed position exists when dart 220 is positioned so as to retard gas or liquid from freely flowing through the generally hollow interior 200 of the plunger. (Note, in this embodiment, the upper surface of the dart is machined to snuggly mate with the lower opening of the plunger body so that more pressure builds below the plunger when the dart is in its closed position than when the dart is in its open position.)

As further depicted by FIG. 2, cage 210 employs clutch 230 to retard movement of dart 220 between its open and closed position. Clutch 230 can be any mechanism known to those skilled in the art for retarding the movement of dart 220, preferably including either one or more c-clips and/or one or more o-rings. In other words, the friction imparted by clutch 230 on the outside surface(s) of dart 220 keeps dart 220 from freely sliding between its open and closed position. This is important because, as described above, proper (or efficient) operation of plunger 100 requires that dart 220 generally remain in its open position as the plunger free-falls down the well, and that dart 220 generally remain in its closed position as the plunger rises in the well. Clutch 230 also should be tuned (in terms of the amount of force it exerts on dart 220) so that dart 220 generally remains in its open or closed position as the plunger travels down or up the well, respectively, but also so that it is able to be moved from its closed to its open position when the plunger reaches the surface of the well, and moved from is open to its closed position when the plunger reaches the bottom of the well.

An exemplary embodiment of dart 220 is more specifically depicted by FIG. 3. As shown, dart 220 comprises upper end 300 and lower end 310. Disposed between upper end 300 and lower end 310 is body 320. Body 320 is sized to have at least one surface raised relative to its surrounding or adjacent surface(s). For example, in the circumstance/embodiment where a cross-section of body 320 is circular, the diameter of the raised surface is greater than the diameter of its surrounding or adjacent surface(s). In this embodiment, and as described in more detail below, the effect of the raised surface impacts the life of clutch 230 and, therefore, the life of the dart bypass plunger itself.

Specifically, in this particular embodiment, the raised and lower surfaces of body 320 for dart 220 have the effect of (1) exerting less force on clutch 230 when clutch 230 is engaged with a lower surface of body 320 and (2) exerting more force on clutch 230 when clutch 230 is engaged with a raised surface of body 320. Put another way, due to the engagement between clutch 230 and body 320, clutch 230 exerts more force on the raised surface of body 320 than it does on the lower surface of body 320.

Still further, in this embodiment, the raised and lower surfaces of body 320 are positioned relative to one another so that clutch 230 effectively applies less force to body 320 when dart 220 is in its open and/or closed position. In other words, clutch 230 will be positioned relative to a lower surface of body 320 when dart 220 is open and/or closed. The longer clutch 230 is exerting less force on body 320 than it is otherwise capable of exerting, the longer clutch 230 will continue to effectively operate before it wears out. And, since dart 220 is in its open or closed position (thereby reducing the force clutch 230 exerts on body 320) more often than it is between such positions (thereby increasing the force clutch 230 exerts on body 320), the longer this design will enable clutch 230 to last before wearing out.

FIG. 4 depicts another exemplary embodiment of a dart, this one shown as dart 400. As shown, dart 400 includes upper end 300 and lower end 310. Disposed between upper end 300 and lower end 310 is the body of dart 400. In this embodiment, the body comprises two separate raised surfaces, 410 and 420 respectively. These raised surfaces function similar to the one raised surface in FIG. 3. Specifically, as shown in FIGS. 6 and 7, raised surface 420 operates (in conjunction with clutch 230) to hold dart 400 in its closed position. Likewise, as shown in FIGS. 8 and 9, raised surface 410 operates (in conjunction with clutch 230) to hold dart 400 in its open position. Raised surfaces 410 and 420 preferably, but need not, have the same outside diameters.

As it was with respect to the one raised surface in FIG. 3, the two raised surfaces 410 and 420 in FIG. 4 (relative to their adjacent surfaces) have the effect of reducing the amount of strain placed on clutch 230 when dart 400 is in its open and closed positions. Moreover, the reduced diameter of dart 400 between raised surfaces 410 and 420 has the further benefit of prolonging the life of clutch 230 by (1) reducing the strain placed on the clutch as the dart transitions between its open and closed positions and (2) reducing the abrasive force that contaminants on the dart impart to the clutch during such transitions, which can unduly wear the clutch, especially if an o-ring is employed as the clutch mechanism.

Since clutch wear often is a limiting factor in the life of an auto-cycling plunger, the above-described designs prolong the life of the plunger, thereby saving equipment costs and well down-time (to replace the plunger) and collectively improve the efficiency of operating the well itself.

FIG. 5 depicts yet another embodiment of the dart for a dart bypass plunger. While FIG. 5 shows dart 500 having two raised surfaces between upper end 300 and lower end 310 (as shown in FIG. 4), it need not include them, or any raised surface for that matter. The embodiment of FIG. 5 does, however, include channel 510 that runs from lower end 310 toward upper end 300. At the upper portion of channel 510, diversion channels 520 and 530 exit on opposite sides of the dart. While two diversion channels are shown, less or more are possible and are within the scope of the present invention. Likewise, while not shown in FIG. 5, one or more other diversion channels are preferably formed as pathways from channel 510 to the exterior of the dart. These other channels are depicted as channel 540 in FIGS. 6-9. Channel 540 is preferably, but not necessarily, offset by 90 degrees from channels 520 and 530. In this manner, flow of the well (whether it be gas or liquid) is able to travel into channel 510 at its opening in the lower end 310 of the dart and exit one or more of the diversion channels 520, 530, and/or 540.

FIGS. 6 and 7 show yet another exemplary embodiment of the present invention. In this embodiment, the lower end of the dart has a reduced outside diameter to provide a gap or space between the outside, lower end of the dart and the inside diameter of cage 210. This reduced outside diameter also is depicted in FIG. 4 at the portion of the dart below raised surface 420. While FIGS. 6 and 7 show the dart depicted in FIG. 5, any dart will suffice so long as its lower end has a reduced outside diameter that provides a gap or space between the outside, lower end of the dart and the inside diameter of cage 210. The amount of space between the outside, lower end of the dart and the inside diameter of cage 210 should be sufficient to allow gas or liquid to flow through that space and out port 610 in cage 210. While FIG. 6 shows only one port 610, a preferred embodiment of the invention includes three such ports, each offset from one another by 120 degrees. This flow operates to cleanse debris that might otherwise become lodged between the dart and the cage and that would, as a result, detrimentally restrict the dart from sliding between its open and closed positions and also unduly wear clutch 230, especially if an o-ring is deployed as the clutch mechanism.

In yet another embodiment of the present invention, channels 510, 520, 530, and 540 operate to create passageways through which gas and/or liquids flow. Specifically, as the dart bypass plunger travels up or down the well, gas and/or liquids travel into channel 510 at the lower end of the dart and exit the dart through channels 520, 530, and/or 540. The turbulent nature of the exiting gas/liquids acts to cleanse or otherwise dislodge contaminants from the outside surface of the dart and from the interface between the dart and its cage. The beneficial effects of this turbulent flow are similar to those described above for the flow that takes place in the space between the outside, lower end of the dart and the inside diameter of cage 210.

As indicated above, it should be understood that this description is not intended to limit the invention. On the contrary, the exemplary embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the exemplary embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art will understand that various embodiments may be practiced without such specific details.

Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein.

This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims. 

What is claimed is:
 1. A plunger assembly, comprising: (a) a plunger having a first and second end; (b) a cage attached to the second end of the plunger; and (c) a dart disposed within said cage having a body with at least two surfaces, where one surface is a raised surface relative to the other, lower surface.
 2. The plunger assembly of claim 1 wherein the dart is slidably mounted in the cage so that the dart can be positioned in at least an open or closed position relative to the second end of the plunger.
 3. The plunger assembly of claim 2 wherein the cage includes a clutch to retard movement of the dart between its open and its closed position.
 4. The plunger assembly of claim 3 wherein the body of the dart is disposed between an upper end of the dart and a lower end of the dart.
 5. The plunger assembly of claim 4 wherein the clutch exerts more force on the raised surface of the body of the dart than it does on the lower surface of the body of the dart.
 6. The plunger assembly of claim 5 wherein the raised and lower surfaces of the body of the dart are positioned relative to one another so that the clutch exerts less force on the body of the dart when the dart is in its open and/or closed position.
 7. The plunger assembly of claim 6 wherein the body of the dart has a circular cross-section and the diameter of the raised surface is greater than the diameter of the lower surface.
 8. The plunger assembly of claim 7 wherein the clutch comprises one or more c-clips.
 9. The plunger assembly of claim 7 wherein the clutch comprises one or more o-rings.
 10. The plunger assembly of claim 9 wherein the cage includes only one set of threads, which connect the cage to the second end of the plunger.
 11. A plunger assembly, comprising: (a) a plunger having a first and second end; (b) a cage attached to the second end of the plunger; and (c) a dart disposed within said cage having a body with at least three surfaces, where two surfaces are raised surfaces relative to the third, lower surface.
 12. The plunger assembly of claim 11 wherein the cage includes at least one channel that allows gases or liquids to pass from inside the cage to outside the cage.
 13. The plunger assembly of claim 12 further comprising a gap between a lower end of the dart and a lower end of the cage that allows gases or liquids to flow through the gap and out the at least one channel in the cage.
 14. A dart for a plunger assembly wherein the dart comprises: (a) an upper end and a lower end; (b) a main channel that runs from the lower end toward the upper end; and (c) a diversion channel that intersects the main channel and provides a passage from an interior of the dart to an exterior. 